451 All MX servers are unavailable for domain comcast.net

Anybody else seen this error on outbound messages? 451 All MX servers are unavailable for domain comcast.net

Several of our users are experiencing problems when sending to comcast.net. They get the message bounced back. Others are fine and able to deliever. So it seems hit or miss and has been happening over the last three days or so.

The knowledge base indicates the error as the following:

This error indicates that all MX servers were unreachable for the destination. If you are receiving this error sending mail TO a domain, please verify that DNS servers are reliably responding.

Please note that if DNS servers are intermittently failing, the verification you perform at that moment may not be indicative of the performance at the time the message was sent.

If this error has happened when mail was being sent TO your domain filtered by the McAfee service, this indicates that we are not able to reach your Inbound Server. Please confirm the destination server is reachable or engaged your Disaster Recovery service.

Am I wrong in thinking that if there is a DNS problem that needs to be verified and corrected that it would be McAfee's DNS servers or Comcast's MX records?

I have opened a ticket with support, but I am curious if anyone else has seen this with either comcast or other domains?

Re: 451 All MX servers are unavailable for domain comcast.net

We had an issue late yesterday and early today where Comcast had one or more McAfee IPs on their blacklist. Our operations team was able to work with Comcast to get those removed, and everything should be working fine now. Those errors are temp-fails, so the messages will be retried for up to 5 days.

Re: 451 All MX servers are unavailable for domain comcast.net

We had an issue late yesterday and early today where Comcast had one or more McAfee IPs on their blacklist. Our operations team was able to work with Comcast to get those removed, and everything should be working fine now. Those errors are temp-fails, so the messages will be retried for up to 5 days.